Loud acoustic condenser



June 24, 1930. P. E. EDELMALN LOUD ACOUSTIC CONDENSER 'Filed July 19, 1929 f @@@f-I? Patented June v24; 1930 UNITED s;Tart:s

,Pari-* Nr ori-lcs PHILIP E. IEHJELMAN, CHICAGO; ILLINOIS, AiSSIGNOR T EPHRAIM BANNING, 0F

CHICAGO,

ILLINOIS v LOUD ACOUSTIC CCNDENSEB.

appneatign'iea July 19, 1929. sefiaim. 379,359.

' In acoustic condensers of `the type shown i and described in my pending application, Serial N o. 352,201, there is a tendency ofthe i flexible sheets forming the electrodes of the condenser to produce a'rustling sound when the loud speakeris going full blast.

An, object of this invention is to provide a means whereby this rustling sound will be decreased, if not eliminated.

Anotherobject is to improve 'the volume' and quality of the sound produced by acoustic condensers. This and other objects, as will hereinafter appear, are accomplished by` this invention which is fully described in the following specication, and shown in the accompany-- y ing drawings, in which- Figure 1 is a transversesectionalview through an acoustic condenser .embodying the invention;

Fig. 2 is a partial slightly l.enlar ,'ged view of the same; 1

Fig. 3 is a View similar to Fig. 2 showing a modified form of the invention; and

Fig. 4 isa! partial front elevation on the line 4 of Fig.` 3.

The embodiment illustrated comprises a frame 10, preferably'of wood,and rectangular inv shape, over which is tightly stretched a flexible metallic 4screen or cloth 11 which is heldin place by a series of screws or tacks 12. Over this is tightly stretched a sheet of iiexible insulating material, as Empire cloth 13, which in turn is held in place by means of a series of screws or tacks 14. v

On the front of the Empirecloth 13 issecured a. thin sheet metal -electrode 15 of tinfoil, sheet aluminum, or the like, by means of a suitable adhesive 15a. The sheet 15 has a connector 16,while a connector 17 is connected to the metal cloth or screen 11.` By means of these thel acoustic condenser may be connected to the out ut circuit of a vradio receiving set or'of a p onograph vamplifier in a well-known'man11e1 .A A fine metal screen, tinsel' cloth, or the like may be used as the base vfor -the backv` electrode 11, and the term metal fabric properties. Upon the metal fabric 11 ismounted a series of parallel strips of metal A18, shown enlarged in Fig. 3. vThese strips .suitable cement, as sodium silicate. A s uitable solder for-,this purpose consists of one `part tin, one part lead, andone part bismuth,

with a rosin flux.

On top of each strip 18 is placed a second andnarrower strip 19of metal which is se- 'cured thereto, preferably centrally by means of solder or cement 20.

Both theEmpire cloth 13 and the metal fabric 11 aretightly stretched over the `frame so that the back of the Empire cloth 13 isv normally 'held closely adjacent to the outermost strlps 19, if not actually in contact therewith, particularly as the electrodes l1 and 15 are maintained under-a normalpotential, difference which tends to draw themtogether.. For the vsake of illustration, however, the Empire cloth 13 is shown in a raised' position, which, however, does notI f exist in actual practice. The thickness of theparts is also greatly exaggerated.

The vforegoing acoustic condenser is found ,to give very .excellent results, and-particularly will standheavy pulsating currents without any perceptible amount of flutter, such'asvwas sometimes previously noted, particularly where a heavy current was used d ue to veryA great amplification, or the like.

, It is believed that this result is due veryv largely tothe fact that the narrower stri s 19 normally pressed against the back of t e empire cloth 13, and as the 'applied potential varies due to the'pulsations therein the attraction ofthe electrodes 11 and 15 for each other Was varied, and this variation causes these electrodes toapproach or recede from each other strips 19. f

The result is that a vbending action'takes 7 place in. both the electrodes causing them 'to' bend 1n a series of waves parallel to and between 'the strips 19, While this bending yis very slight, it'takesplace over a very large a'.1 ea,i1and4 as a result,thel volume ofvsound principally between the g ln Fig. 2 is shown a idea 1n which three strips are superimposed i .closely adjacent produced is. great and is or a very excellent tone quality.

lt is :tound in Fig. 3 3%, `in Width and spaced l, making the spacing from center to -center oithe strips i9 about While the top'strips 19 are egg in vvidth.

that the strips 18 as arranged roodication ci this and secured to each other one'upon7 the other, h

in substantially-the and to the metal 'fabric saine Wav'. lt Will be understood that the metal strips maybe' rolled or otherwise formed so as to be integral vvith the center made higher thanv the edges togive substantially the 'saine re.

sult. l l While l have ldescribed and shown but a i'evv embodiments ci roy invention, it is to be understood that it is capable of many ineditications. Changes, therefore, in the construction and arrangement may be rnade which do not depart 'from the spirit and scope or' the invention as disclosed in the appended claims.

ll clairn:

Il. ln condenser speaker, a ilenible back electrode, a flexible sheet insulator positioned closely 'adjacent to the iront tace oi` the back electrode, a 'front electrode mounted on the iront side of said insulator, said back velectrode having a series oi spacedraised projectionsto prevent the insulator from norrnalljl contacting vvith the back electrode over a large portion of the area at one time.

2. ln a condenser speaker, a flexible back electrode, a dexible sheet insulator positioned to the iront face ot' the back electrode, a front electrode'mounted on they front side ci said insulator, said baclr electrode having a series of spaced raised `projections `to prevent the insulator 'trom' normally contacting vvith the back electrode over a large portion of the area at one time,

said back electrode having air spaces betvveen said projections.

3. .lin a condenser speaker, a flexible back electrode, a exible sheet insulator positioned closely adjacent tothe front face ci the baclr electrode, a 'irontv electrode mounted on the iront -side ci said insulator,` said' back electrode having a series ci 'spaced raised substantiallj/vv parallel ridges to prevent the insulator from normally contacting vvith'the back electrode over a1large'portionci' 'the area at one time, said back electrodev having air spaces between said projactions.`

4:. ln a condenser speaker, a flexible back electrode, a flexible. sheet insulator positionedclosely adjacent to the iront aceoi the baclr electrode,'a front electrode inount-l ed on the iront side of said insulator,- said baclr electrode having a series ot spaced raised substantially parallel ridges ot metal "will vvorlr very well when rnade j aggiornano to prevent theinsulator 'from normally con-- /tacting vvith the back electrode over a large portion of the area at one time, said back electrode having air spaces between said projections.

5.- .ln a 'condenser speaker, a back electrode comprising1 a metal fabric having a series' of spaced parallelv metal strips secured thereto, the center ci said strips being higher than the side edges, a exible insulating diaphragm, and a iront metal electrode on said diaphragm..

(i. ln an acoustic reproducer, a sound diaphragrn comprising a porousdenible member provided vvity a plurality et substantiallj/ parallel spaced electrode elements, and a cooperating member Astretched. adjacent thereto. 4

'Tyr-ln acoustic condenser consisting of a vdielectric diaphragm, an electrode therefor,-

a col-operating electrede diaphragm therefor, and means to retard the return rnovenient thereof comprising 'an air compression section therebetween proportioned 'to retard the return movement the morethe greater the :torce applied'l thereto.

8. ln an acoustic condenser, a' metal electrode having a series of raised parallel ridges spaced apart a distance of the order of LVS, with openings between said ridges to permit of the passage ci air, a flexible Y diaphragi'nheld in iront ci said electrode and in Contact With said ridges whereby a varying voltage applied to said condenser vvill cause said diaphragm to bend in a' series ci vvaves parallel to .and between said ridges. h

ln testimony whereof, 'have hereunto set my hand this 15th dav of duly, 1929.

l j lllflllall EDELMAN.

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